For older people, gabbing on a cell phone while walking across the street may increase the chances of being run over, according to a new study, although earlier research did not find the same connection among younger people.

Just listening to music on an iPod or other portable device doesn't pack the same risks as talking on a cell phone, the researchers found.

The results are based on two lab-based studies in which participants had to maneuver on a treadmill to cross a virtual street, and so further research is needed to firm up the results in the real world. One possible shortcoming: People may find it more difficult to walk on a manual treadmill than they would on actual concrete. But the simulation allowed researchers to make sure all subjects experienced the exact same conditions.

"Many people assume that walking is so automatic that really nothing will get in the way," Art Kramer, a psychology professor at the University of Illinois who conducted the research, said in a statement. "But actually walking in environments that have lots of obstacles is perhaps not as automatic as one might think."

Previous research in a natural setting found walking and talking on a cell phone so distracting that subjects failed to spot an obvious clown riding a unicycle.

Participants in Kramer's study took their virtual stroll on a manual treadmill that only moves when the person walks. Images of an intersection were projected on three screens placed in front of, to the right and left of the subject. The treadmill was synced up with the virtual environment. Each participant had to complete a jaunt that included crossing a street, with cars, three times: once with no distractions, having a cell-phone conversation, and listening to music on an iPod.

The first, with 36 college students, showed that students trying to hold a phone conversation took 25 percent longer to cross the street compared with those without phones and those listening to iPods. Cell-phone users were also less likely to finish crossing the street in the 30 seconds allotted for the task.

However, the young adults were not more likely to get hit by a virtual car even if they were talking on a cell phone. The study was published online Nov. 5 in the journal Accident Analysis and Prevention.

The researchers note that cell-phone users who didn't finish crossing spent most of their time waiting at the curbside, suggesting they failed to spot safe opportunities to cross the road. In real life, pedestrians do not always have the option to wait — they might be in a hurry to get to work, or running late for an appointment. In such rushed instances, failing to recognize a safe time to cross could have harmful consequences, such as a vehicle collision, the authors write.

The second study, yet to be published, focused on people 60 and older.

"Older adults on the phone got run over about 15 percent more often [than those not on the phone]," Kramer said. Subjects who had a history of falling fared even worse.

"Walking and talking on the phone while old, especially, appears to be dangerous," Kramer said.

But why was music-listening less of a hazard than talking on the phone? The researchers point out that a conversation requires a person to comprehend and respond, while listening to tunes is a more passive activity. They speculate it may be easier for an individual to tune out music to concentrate on the task at hand, while the same cannot be said for chatting on the phone.